Cherubael

Cherubael is a daemon prince once worshipped on Clanar II who spent centuries as Quixos’s weapon and Eisenhorn’s reluctant problem sealed back into flesh.

Quixos bound him. Eisenhorn banished him on Farness Beta, then stuffed him into new hosts because the next fight was worse. He talks like a courtier, kills like a siege engine, and steered Eisenhorn toward radicalism for a long game that almost worked.

Godwyn Fischig became a later cage. Cherubael still answers when Eisenhorn is desperate enough to knock. Desperate is a schedule, not a mood.